In making of a liquid crystal display (LCD) device, sealant materials are often coated and cured in the periphery of an array substrate or a color filter substrate. The sealant material is used to bond the array substrate and the color filter substrate together and to protect the liquid crystals injected into the space between the array substrate and the color filter substrate from being affected by the ambient air and water.
After the array substrate or the color filter substrate is coated with the sealant material, the sealant coating needs to be inspected to detect any occurrences of defects such as a crack or gap (“a” as shown in FIG. 1), a non-uniform line (too thin “b” and too thick “c” as shown in FIG. 1), a spilled drop (“d” as shown in FIG. 1), etc.
In a conventional process, the sealant coating is inspected as follows. In a first step, one or more mark points are configured on the array substrate or the color filter substrate coated with the sealant material. The mark points are usually patterns clearly identifiable in terms of brightness and/or contrast difference under certain pre-configured lighting condition. The sealant material is coated in a graphic pattern to maintain certain position relationship with the mark points. In a second step, an image acquisition unit, e.g., a charge-coupled device (CCD) camera, is used to capture images of the array substrate or the color filter substrate coated with the sealant material under certain pre-configured lighting condition. In a third step, due to the brightness and/or contrast difference, the mark points are easily identifiable from the captured images and the identified positions of the mark points have very small deviations from the actual positions. Based on the relationship between the mark points and the graphic pattern of the sealant coating, the identified positions of the mark points are used to determine the ideal graphic pattern of the sealant coating in the captured images.
In the meantime, the actual graphic pattern of the sealant coating is determined based on the brightness and/or contrast difference. In a fourth step, the actual graphic pattern of the sealant coating from the captured images and the ideal graphic pattern of the sealant coating determined by the mark points are compared to detect any occurrences of defects such as cracks, gaps, non-uniform lines and spilled drops of the coated sealant.
However the above described inspection process has the following drawbacks. Firstly, gate lines, data lines, and other signal lines, thin film transistors, pixel electrodes and other structures are usually formed on the array substrate. Color filters, black matrix, etc. are usually formed on the color filter substrate. These structures may also be captured in the images, may interfere with the mark points, and may cause errors in identifying the mark points and in forming the ideal graphic pattern of the sealant coating. In addition, these structures may also interfere with the actual graphic pattern of the sealant coating when being identified. The area that does not include the sealant coating may be undesirably recognized as being coated with the sealant material, which includes over-identification or false identification. On the other hand, the area that does include the sealant coating may not be recognized as being coated with the sealant material, which includes under-identification. Thus, the inspection results have significant deviations and are considered as unreliable.
Secondly, due to the frequent occurrences of the over-identifications and under-identifications in the inspection results, on-site human intervention is required to refine the parameters of the sealant coating process. Thus, more time is then needed and the productivity of the sealant coating process is reduced.
Finally, the above inspection process of the sealant coating does not assure the pre-configured lighting condition of the light sources, nor monitors the status of the image acquisition unit. When the substrate illumination changes, for example, the light intensity of the light sources decreases over time, the image acquisition unit is out of focus, and/or the lens transmittance fluctuates, for example, dust is accumulated on the lens surface of the CCD camera. The captured images may not accurately reflect the actual graphic pattern of the sealant coating. Thus, the inspection result concluded from the captured images is unreliable.
The disclosed method and device for sealant coating inspection are directed to at least partially solve one or more problems set forth above and other problems in the art.